On the effects of spreading sequences over MIMO systems

In this paper, we develop a Software Defined Radio (SDR) test bed to evaluate the Multiple Access Interference (MAI) effects over SISO and 2×MIMO systems. It can be observed that under asynchronous transmissions, the Gold code leads to the best performance over both systems due to the fact that it has the best correlation properties. We also find the MAI effects in terms of the spreading sequences pairs on MIMO-STS systems. We propose a criterion for selecting promising spreading sequences for MIMO systems. Based on the measured results, we identify pairs of spreading sequences which have improved BER compared to other pairs in the same set of spreading sequences. We infer that the choice of spreading sequence pairs in a MIMO-STS system in the presence of MAI sources is an important factor to be considered.